Application Variables that Affect Efficacy of Disinfestants Sprayed on Different Substrate Materials to Control Colletotrichum Siamense

Authors: Copes, Warren; Read, Quentin; Smith, Barbara

Submitted to: PhytoFrontiers
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/3/2025
Publication Date: 4/7/2025
Citation: Copes, W.E., Read, Q.D., Smith, B.J. 2025. Application Variables that Affect Efficacy of Disinfestants Sprayed on Different Substrate Materials to Control Colletotrichum Siamense. PhytoFrontiers. https://doi.org/10.1094/PHYTOFR-12-24-0131-R.
DOI: https://doi.org/10.1094/PHYTOFR-12-24-0131-R

Interpretive Summary: Disinfestants are an important sanitation tool used to eliminate plant pathogens. Instructions for the usage of disinfestant products can be found on product labels, University Extension bulletins and the internet. These sources provide the information currently known for obtaining proper efficacy. A review of research has shown inconsistencies in efficacy are possible even when following these information sources. A series of studies were performed to investigate the reliability of six disinfestants in controlling Colletotrichum siamense present on six substrate materials. All six disinfestants provided effective control of C. siamense when applied to three non-porous substrate materials (4-mil plastic sheet, galvanized metal and greenhouse polycarbonate twin-wall). Contact time as short as 1 min was effective on the non-porous materials. In contrast, control tended to be poorer for most of the six disinfestants when applied to three porous substrates (concrete, ground fabric and non-treated pine wood). Contact time as long as 20 min didn’t improve the control outcomes. Two sequential applications of the label recommended dose of a disinfestant improved control on porous substrates compared to one application of a doubled-label dose, in most cases. This research identifies some substrate materials that are easier and more difficult to disinfest and provides alternative disinfestant treatments to improve efficacy. The information will be useful to horticultural producers and crop advisors that deal with eliminating plant pathogens from ornamental plant production surfaces.

Technical Abstract: Disinfestants are an important sanitation tool used to eliminate plant pathogens. Disinfestant product labels, as well as University and company literature, provide instructions and guidance for the proper usage of disinfestants, yet recent research has shown inconsistencies in efficacy are possible even when following these information sources. The efficacy of a selection of hypochlorite, isopropyl alcohol, quaternary ammonium and peroxygen compounds against Colletotrichum siamense was evaluated in a series of seven in vitro studies relative to substrate porosity, contact time and wettability properties when sprayed on six substrate materials (concrete, galvanized metal, polypropylene ground fabric, polyethylene plastic sheet, pressure-treated pine, and twin-wall clear polycarbonate) representative of ornamental plant production surfaces. Bayesian generalized linear mixed models were used to calculate posterior distributions of the median point estimate and 95% equal-tailed credible intervals representing uncertainty about the means. Control of C. siamense was consistently achieved on the three nonporous substrate materials with all six disinfestants, but the level of control was variable when treating porous substrate materials. Contact time, within the range of 1 to 20 min, and spray coverage differences between spreading and beading disinfestants were not prominent factors that affected efficacy. Both two sequential applications of a label dose and one application of a high dose potentially improved control outcomes, although two applications of a label dose, which does not violate disinfestant product label guidance, more consistently achieved the lowest median recovery of C. siamense.